To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The logic devices used in smart phones drive forward the miniaturization technology. Logic devices of 10-nm node are manufactured in a large scale using a multi-patterning lithography process based on ArF lithography.
In the application of lithography to next 7-nm or 5-nm node devices, the increased expense and overlay accuracy of multi-patterning lithography become tangible. The advent of EUV lithography capable of reducing the number of exposures is expected.
Since the wavelength (13.5 nm) of extreme ultraviolet (EUV) is shorter than 1/10 of the wavelength (193 nm) of ArF excimer laser, the EUV lithography achieves a high light contrast, from which a high resolution is expectable. Because of the short wavelength and high energy density of EUV, an acid generator is sensitive to a small dose of photons. It is believed that the number of photons available with EUV exposure is 1/14 of that of ArF exposure. In the EUV lithography, the phenomenon that the edge roughness (LWR) of line patterns or the critical dimension uniformity (CDU) of hole patterns is degraded by a variation of photon number is considered a problem (see Non-Patent Document 1).
As the pattern feature size is reduced, the LWR of line patterns and the CDU of hole patterns are regarded significant. It is pointed out that these factors are affected by the segregation or agglomeration of a base polymer and acid generator and the diffusion of generated acid. There is a tendency that LWR becomes greater as the resist film becomes thinner. A film thickness reduction to comply with the progress of size reduction causes a degradation of LWR, which becomes a serious problem.
The EUV lithography resist must meet high sensitivity, high resolution and low LWR at the same time. As the acid diffusion distance is reduced, LWR is reduced, but sensitivity becomes lower. For example, as the PEB temperature is lowered, the outcome is a reduced LWR, but a lower sensitivity. As the amount of quencher added is increased, the outcome is a reduced LWR, but a lower sensitivity. It is necessary to overcome the tradeoff relation between sensitivity and LWR.